Longitudinal resonance for thin film ferromagnets with random anisotropy

At the microscopic level, individual spins in ferromagnets with random anisotropy tip transversely with distinct local angles relative to the magnetization → M. When driven by an rf field along the equilibrium → M0, which changes d M = ˆ M0 ⋅ d → M, the transverse tippings rotate about → M0, corresp...

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Bibliographic Details
Published in:Physical review. B 2018-12, Vol.98 (21), p.1, Article 214415
Main Authors: Saslow, Wayne M., Sun, Chen
Format: Article
Language:English
Subjects:
Anisotropy
Demagnetization
Ferromagnetism
Resonators
Thin films
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Summary:At the microscopic level, individual spins in ferromagnets with random anisotropy tip transversely with distinct local angles relative to the magnetization → M. When driven by an rf field along the equilibrium → M0, which changes d M = ˆ M0 ⋅ d → M, the transverse tippings rotate about → M0, corresponding to a new macroscopic collective angle ϕ about → M0. The coupling of d M and ϕ leads to a new longitudinal mode that in bulk has a frequency that is largely independent of field H. A longitudinal mode has been observed in thin films of ferromagnets with random anisotropy, but its frequency is H dependent; for H at angle θ to the film normal and fixed resonator frequency f, H cos θ was constant to angles of 80 ∘, with H saturating for larger angles. When the demagnetization field is included the theory yields such an H vs θ for θ < 80 ∘, thus providing evidence for the predicted angle ϕ. However, lower frequency resonators are needed to manifest the predicted macroscopic anisotropy energy.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.98.214415